Heretofore, in bag manufacturing devices, the film is fed intermittently and sealed by sealer to make a bag.
FIG. 2 shows a front view of a prior art device comprised of a film supplying part 1, film driving part 2, and bag pick up part 3.
In film supplying part 1, film 4 is taken from film roll 10, folded along the center line by folding device 11, and fed intermittently through dancer or damper roll section 12.
Film driving part 2 comprises a pair of intermittent feed rollers 20, 21. As shown in FIG. 4, lower feed roll 21 is connected to crank 36 through shaft 22, pulley 23, timing belt 24, pulley 25, output shaft 26, electromagnetic brake 27, electromagnetic clutch 28, pinion shaft 29, pinion 30, spur gear 31, pinion 32, sector gear 33, pin 34, and connecting rod 35.
In crank 36, arm 38 of U-shaped cross section is fixed to drive shaft 37 of a motor (not shown). Screw 39 is supported in arm 38, and nut block 40 is mounted on screw 39 so as to move along its axis upon rotation of screw 39. Connecting rod 35 is connected to nut block 40 through pin 41.
As shown in FIG. 2, sealer 42 and sealing roller 43 are provided at the front of feed rollers 20, 21, shown in FIG. 1. Sealing cams 44, 44 are fixed on drive shaft 37 for actuating sealer 42 up and down.
Bag pick up part 3 is substantially the same as that of Japanese Patent Application 60-29164 which is not an essential part of this invention so a detailed explanation of this part is not included.
The operation of the device is as follows:
As shown in FIG. 4, upon rotation of drive shaft 37, arm 38 rotates, pinion shaft 29 rotates through operation of connecting rod 35, sector gear 33, pinion 32, spur gear 31, and pinion 30. When pinion shaft 29 rotates in a counter clockwise direction, clutch 28 is connected and brake 27 is inactive. In contrast, when pinion shaft 29 rotates in a reverse direction, clutch 28 is inactive and brake 27 is active. Therefore, feed rollers 20, 21 rotate intermittently. Clutch 28 and brake 27 are controlled at high speed for accurate film feed pitch, being active and inactive repeatedly at high speed.
Sealer 42 is moved up and down by sealing cam 44, 44 attached to drive shaft 37, as shown in FIG. 1, in syncronization with intermittent feed of film 4 by feed rollers 20, 21, and seals and cuts film 4 when it is stopped, to produce a bag 4a.
In the case of unprinted film, upper dead point (.theta.=180 degrees in FIG. 4) and lower dead point (.theta.=0 degrees in FIG. 4) of crank 36 and rod 35 are detected by timing cam (not shown) and a limit switch or contactless switch etc., and the detecting signal is fed to clutch 28 and brake 27 to operate them. Alternatively, an encoder is fixed on shaft 37 which may generate similar signals. The feed pitch of film 4 is determined by the eccentric distance of crank 36.
In the case of printed film, as shown in FIG. 2, photoelectric detector 45 is supported above the running face of film 4 for detecting a printed pattern or special eye or registration mark for detecting the film feed pitch. The detecting range of the detector is limited by a timing cam or decoder to avoid error due to another print or dirt. The detected signal "t" of detector 45 is fed to clutch 28 and brake 27 through high speed control unit 46, so as to seal and cut film 4 in registration with the printed pattern or eye mark. The eccentric distance of the crank is set to feed the film by a distance which is a little in excess of distance "d" larger than the pitch of the print for assuring passage of eye mark under detector 45. By this setting, the eye mark is sure to pass under detector 45. Detector 45 detects the eye mark and sends a signal "t" for disconnecting clutch 28 and operating brake 27. For this reason, detector 45 operates a little prior or beyond the lower dead point of crank 36.
Thus, the light spot on the head of detector 45 detects a printed mark or eye mark and stops the feed of film 4, and accuracy of the width of bag 4a is improved.
However, the accuracy of printed marks is not good, and their pitch varies. Moreover, the pitch of the mark varies according to the stretching of film 4 during manufacturing. Recently the tendency has increased according to a larger diameter of the film roll. If the pitch of the mark increases, the mark does not come into the detecting range of detector 45, (i.e. the spot of light or head due to the lack of the feed of the film), so that control of the detector fails and makes many defective bags before an operator discovers it. Otherwise, if the pitch becomes shorter, distance "d" becomes larger, the actuating point of brake 27 is offset from the lower dead point of crank 36, and a rapid stop during the rotation of output shaft 26, clutch 28, brake 27, feed rollers 20, 21, sealing roller 43 is repeated which wears on clutch 28 and brake 27, and shortens their life. It also increases the noise of the machine, accuracy of the width of a bag 4a becomes bad, and lowering the quality of the bags.
To prevent these drawbacks, an operator inspects the operation and can not do any other work. When the pitch of the mark becomes shorter, the excess distance "d" should be adjusted, but the amount of the excess distance "d" is not clear and setting it to a larger amount might cause the former drawback to occur.
To set the excess distance "d", as shown in FIG. 3b, crank 36 should be rotated to a position where a special handle can be inserted into screw 39 of crank 36, then the handle is rotated while watching the position of crank 36. Then, by rotating crank 36, one of friction blocks 14 and 15 provided on a special fine adjusting handle 13 engages toothed gear 16 provided at the end of screw 39 and rotates gear 16 and screw 39 in a clockwise or counter-clockwise direction. This moves nut block 40 and pin 41 and the eccentric distance of the crank can be adjusted. The adjustment is repeated until the feed pitch reaches the right value. On the other hand, film 4 is set to be fed a somewhat longer pitch than the pitch of the mark under an inactive state of detector 45. Then the head of detector 45 is put on the passing line of the mark and actuates detector 45 for controlling clutch 28 and brake 27.
However, the above mentioned adjusting operation is hard for unskilled workers and a great loss of bags occur.